1. Field of the Invention
The present invention relates to the combination of recordable-reproduceable optical discs and reproducing-only optical discs and an optical disc player which is capable of reproducing recorded signals both from the recordable-reproduceable optical disc possessing pregrooves and the reproducing-only optical disc possessing recording pits by means of a common optical system having a common laser.
2. Description of the Prior Art
A recordable optical disc can record and reproduce signals by using a semiconductor laser in a recording layer containing, for example, tellurium oxide, and the signals are recorded in a contrast pattern as a change in the reflectivity. Pregrooves showing the recording tracks are preliminarily provided in the optical disc for raising the recording density and facilitating the recording and playing operation. By detecting these pregrooves, signals are recorded and reproduced on the pregrooves.
On the other hand, the reproducing-only disc is manufactured as follows: the master board of a reproducing-only disc is a glass board, on which photoresist is applied, and the light source or argon laser beam is modulated by a photo modulator, and signals are recorded. From the recorded master board, a stamper is prepared through the developing process and plating process, and a replica disc is made from this stamper by using a press. A reflection plane is evaporated to this replica disc, and a reproducing-only disc is thus complete. In the thus manufactured reproducing-only disc, signals are recorded in tiny undulated patterns (called signal pits).
Thus, the reproducing-only disc and recordable optical disc are basically different in their characteristics. Conventionally, these recordable discs and reproducing-only disc were of different systems, and were not related to each other, so that they could not be reproduced commonly by the same optical system.